More power to you if you feel the need to use a SPL meter, I just don't see the need. Music where instruments are plugged in should be played Medium to loud.
I lived very well without my SPL too, but going WAY back I've always had the Radio Shack meter around to verify home theater voicing, checking individual drivers for equal output, reporting to others about how loud a hum or buzz is from a transformer that's supposed to be quiet and even measuring the SPL from various record cleaning machines to see if "quietness" claims are accurate.
I even use it occasionally to prove to my wife that a favorite restaurant is probably in violation of OSHA on Saturday evening :^), for amusement if nothing else.
SPL meters are like speedometers on cars, we all know when we're driving way too fast, but it's nice to know how much over.